“He said he’s come across many cases where a young, uneducated person had been arrested for a terrible crime and just confessed, wrongly.”Malone added “alarm bells” had started ringing from the first words of Evans’ confession, where he told police: “I’ve disposed of my wife down a drain.”“That felt like a learnt phrase, not something he would have said himself,” she said. “A lot of the language used in his statement Gregg said didn’t sound like Tim’s language.“A big part of the case against him was that he knew more information than he should have known, but Gregg believes the police knowingly or unknowingly said that information to him in the long, overnight interviews.”The three-part drama is to be broadcast on BBC One later this month. Samantha Morton as Ethel ChristieCredit:BBC As well as speaking to family, writers also called on McCrary to shed light on criminal behaviour, handing him transcripts, court reports and autopsies from the 1950 case in a bid to shed light on why Evans initially confessed.After studying the material, McCrary confirmed he believed Christie had carried out all of the murders, with key similarities between them.Whitmore said: “Gregg said to an educated person, the idea of someone confessing to a crime they haven’t committed is bizarre and extraordinary and suspicious.“But he said the point is when you have these people under pressure for hours or days on end, they’ll do anything to make it stop. They’ll do anything to have a release from that. Writers Ed Whitmore and Tracey Malone told the Telegraph they had been determined to reveal how Christie had convinced police and jury he was an upstanding member of society, while the less well-educated Evans was left to hang.In particular, they said, they had spent an “emotional” afternoon with Evans’ elderly half sister Mary, who claimed police had turned away key evidence from his siblings at the time of the investigation.Malone said: “His half-sister told us how she would babysit the baby sometimes, and they had been alone in the house when Christie would creep in. It really brought it home, hearing it from her.“After everything that happened, she and her sister were told different stories by Ethel and Christie about what had happened to Beryl and where she’d gone. Timothy Evans who was hanged for the murder of his baby daughter Geraline Evans Jodie Comer and Nico Mirallegro as Beryl and Timothy EvansCredit:BBC Tim Roth as John Christie in the BBC dramaCredit:BBC “She tried to tell the police this and they didn’t want to listen. They just thought they were young girls.“That was another frustration: had they [police] listened to some of those things, they might have come to a different conclusion.”She added: “There are a lot of inconsistencies in the police work. There were builders in the house and there worksheets went missing, conveniently.“Autopsy information was withheld because they felt it was too distasteful for the courtroom.” John Christie, the serial killerCredit:PA It is now widely believed the murders were in fact carried out by John Christie, who strangled at least eight women in his London home before burying them in the garden, in the walls and under floorboards in his home.The drama will depict the relationship between Christie, played by Roth, and wife Ethel, who is seen growing increasingly suspicious behaviour while lying for him amid the horror of domestic abuse before eventually being strangled herself.The family of Evans have long campaigned to have his conviction overturned, with several high-level investigations into the miscarriage of justice. Evans’ case has since become a central part of the argument against capital punishment. It is one of the most notorious miscarriages of justice in British legal history, resulting in an innocent man being put to death for a grisly murder he did not commit.Now, the BBC is to shed new light on the serial killings at Rillington Place, after calling in one of the FBI’s star investigators to comb through the evidence.Rillington Place, a new drama starring Tim Roth and Samantha Morton, will be based on extensive research pieced together between the family of the innocent man, written archives and the expert opinion of former FBI agent Gregg McCrary.It will tell the story of how Timothy Evans, the young husband of murdered Beryl Evans and their daughter Geraldine, was hanged after an erroneous confession police failed to see through. Want the best of The Telegraph direct to your email and WhatsApp? Sign up to our free twice-daily Front Page newsletter and new audio briefings.